Journal ArticleDOI
Effect of gusty inflow on the jet-switching characteristics of a plunging foil
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In this article, the effect of stochastic inflow fluctuations on the jet-switching characteristics of a harmonically plunging elliptic foil at a low Reynolds number regime has been analyzed.Abstract:
The effect of stochastic inflow fluctuations on the jet-switching characteristics of a harmonically plunging elliptic foil at a low Reynolds number regime has been analyzed in the present study. The inflow fluctuations are generated by simulating an Ornstein–Uhlenbeck process—a stationary Gauss–Markov process—with a chosen correlation function. In the absence of fluctuations, quasi-periodic movement of the wake vortices plays a key role in bringing out jet-switching at κh ≥ 1.5. However, fluctuating inflow alters the organized arrangement of the vortex street even at a lower κh (κh = 1.0), giving way to an advanced jet-switching onset. More frequent switching with a larger deflection angle is also observed at κh = 1.5 as compared to the no fluctuation case. Effects of inflow timescales on the deflection angle and switching frequency of the wake are investigated by varying the input correlation-lengths. The underlying flow physics are investigated through a qualitative study of the near-field interactions as well as various quantitative measures derived from the unsteady flow-field.read more
Citations
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Transition boundaries and an order-to-chaos map for the flow field past a flapping foil
TL;DR: In this article , an order-to-chaos map for the unsteady flow field of a flapping foil in the low Reynolds number regime is presented, which can capture the physical effect of the parametric variations on the wake dynamics.
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Chordwise flexible aft-tail suppresses jet-switching by reinstating wake periodicity in a flapping foil
TL;DR: In this paper , the effect of a chordwise flexible aft-tail of a rigid heaving aerofoil on the dynamical transitions of the trailing-wake is studied using an in-house fluid-structure interaction (FSI) platform, comprising a discrete forcing immersed boundary method based incompressible Navier-Stokes solver, weakly coupled with a finite difference method based structural solver.
Journal ArticleDOI
Passive dynamics regulates aperiodic transitions in flapping wing systems
TL;DR: In this article , the authors considered the idealized case of a pitching-plunging flapping foil and numerically investigated the effects of passive pitching dynamics on the fluid forces and dynamical states, and compared it with a fully actuated wing.
References
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Journal ArticleDOI
Study of mechanisms and factors that influence the formation of vortical wake of a heaving airfoil
Z. C. Zheng,Zhenglun Alan Wei +1 more
TL;DR: In this paper, a two-dimensional numerical study is performed to investigate the relation between the direction of a deflected wake and the vortex pairing mechanisms, and the deflection angle can be correlated with two effective phase velocities defined to represent the trends of symmetry breaking and symmetry holding, respectively.
Journal ArticleDOI
Dynamics and flight control of a flapping-wing robotic insect in the presence of wind gusts.
Pakpong Chirarattananon,Yufeng Chen,E. Farrell Helbling,Kevin Y. Ma,Richard Cheng,Robert J. Wood +5 more
TL;DR: Simulation of wind disturbances in a laboratory setting and investigation of the flight dynamics of a millimetre-scale flapping-wing robot suggest that modulation of wing kinematics to stabilize the flight in the presence of wind gusts may indirectly contribute an additional stabilizing effect, reducing the time-averaged aerodynamic drag experienced by the robot.
Journal ArticleDOI
Mechanisms of wake deflection angle change behind a heaving airfoil
Zhenglun Alan Wei,Z.C. Zheng +1 more
TL;DR: In this article, an immersed-boundary numerical method is applied to simulate the wake downstream of a two-dimensional heaving airfoil, and a cross-flow effective phase velocity is introduced to analyze the already-formed asymmetric wake behind the air-foil.
Journal ArticleDOI
Plunging Oscillations of Airfoils and Wings: Progress, Opportunities, and Challenges
Ismet Gursul,David Cleaver +1 more
TL;DR: In this paper, the vortex dynamics of thrust and lift generation for periodically plunging airfoils and finite wings at low Reynolds numbers is reviewed, and the effects of vortex lock-in phenomenon, leading-edge vortex, and vortex locking are discussed.
Journal ArticleDOI
Jet meandering by a foil pitching in quiescent fluid
TL;DR: In this article, a rigid symmetric NACA0015 airfoil purely pitching at a fixed location in quiescent fluid is studied using visualizations and particle image velocimetry.